This invention relates to a process for measuring a quantity useful in determining the amount of oil that may be contained within an oil layer or oil column of a dipping reservoir in which there is water or gas at a location not encountered by a borehole. More particularly, the invention relates to a process for directly measuring the formation water pressure at a selected depth within the portion of such an oil column which is encountered by a borehole.
It is known that within such an oil-productive portion of such a reservoir the distance between measuring location and the oil-water interface is proportional to the difference between the oil pressure and the formation water pressure at the measuring location. But, as far as applicants are aware, no method for directly measuring such a water pressure has been previously proposed. Where determinations were previously made of the distance between a point within a borehole and an oil-water interface not encountered by the borehole, the determinations were based on a formation water pressure measured within a water layer encountered in a nearby reservoir. Such determinations were often inaccurate because of the differences in the geological situations.